Urea-formaldehyde-alkyd insulating composition



Patented Nov. 16, 1948 UREA-FORMALDEHYDEALKYD INSULAT- ING COMPOSITXONCharles B. Leape, Pittsburgh, andFrank A. Sattier, Wlknsburg, Pa.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation oflemisylvania.u

Application June-29,. 1944, sei-iai N..542,'14o

This inventionV relates to an insulatin'ggcomDO-v sition, moreparticularly a vwire enamel 'compo-- sition suitable i or use inproducing-insulated electrical conductors.

wire, produced by the use of the composition.

Large quantities of electrical conductor such as copper Wire areelectrically insulated by apply- 6 Claims. (VCI. 260--32.8)

. impregnation, elevated temperatures and reduced pressures may" beemployed in order to insure thorough'penetration and to drive oilthesol- The inventionfurther 'relates to the insulated conductors,especially enameled'.

ing to the surface thereof organic finishes in the form of an enamelcoating. The electrical industry employs enormous quantitiesof enameledwire of this kind in building electrical motors, coils, transformers andrelated apparatus. and service rendered by electrical apparatusemploying the enameled Wire conductor is dependent on the ability of theenamel coating to withstand the operating conditions and atmospheres towhich the apparatus may be subjected. For example, electrical apparatussuch as a motor may heat up to relatively high temperatures whenoverloaded or when employed i'n heated surroundings where cooling may beat a minimum. In other cases, the electrical apparatus may be subjectedto moisture, such, for example, in the form of rain or inadvertentsplashing and the like. Again, the electrical apparatus may be subjectedto highly abrasive conditions which hold in cement mills and othermanufacturing establishments. Corrosive gases may be present, forinstance, in mines, chemical plants, and other manufacturingestablishments. A great variety of conditions may be met with duringwhich the enamel coating may be subjected to both mechanical andchemical deterioration whereby the effective life and service of theapparatus depends primarily upon the quality and nature of the appliedenamel on the conductor.

Furthermore, enameled wire may be subjected to extremely rough usage atthe time it is being applied to and incorporated in an electrical motoror other apparatus. In Winding insulated Wire in motor cores, forinstance, the wire is often applied by means of automatic machines whichstretch, twist and bend the Wire severely. The wire may be subjected toforces which elongate the conductor metal 10% and more in length inAthis operation. Good enamel must stretch with the conductor withoutcracking. After the enameled wire has been applied to apparatus, it isa. common practice in the art to impregnate the apparatus withimpregnating varnishes. These varnishes are composed of resinousmaterials dissolved in any one or more of a variety of solvents, usuallyhydrocarbon liquids such as toluene and naphtha fractions. In theprocess of The life' lll vents from the treated apparatusand'tohardenthe fresinous components of the varnish. Such conditions impose-severerequirements to be met by enamel coatings. A good enamel coating Ishouldnot dissolve, sleeve off the conductor or crack or otherwise signicantlydeteriorate. y

A number of test-s for enameled wire have been developed in the art inorder to determine the characteristics of any enameled wire coating inorder to evaluate its ability tol meet the condtiions of manufacture andsubsequent use. Thus various scrape and abrasion tests havebeendeveloped to indicate the relative toughness and hardness of an enamelcoating. By means of these tests, it is possible to evaluate the abilityof an enamel coating to withstand winding in contact with a relativelyrough metal core slot, its resistance to pounding such as takes placewhen windings are compacted inslot cells of motors, and other mechanicalabuse. The scrape test is particularly significant because it givesinformation on the fundamental property of mechanical toughness andstrength. The test is usually performed by moving the enameled wireunder a loaded'knife edge, the load on the knife edge being increaseduntil the enamel coating is scraped oi the conductor. The weight inounces required to reach the failure point of the coating is designatedas the scrape value. In the `evaluation of the present enamels, thescrape testing devices described in United States Patent No. 2,329,062and the Leape et al. patent application Serial No. 467,736, filedDecember 3, 1942, now Patent 2,372,093, have been employed.

The dielectric strength of an enamel coating is a highly importantfeature. At the present time a minimum of 1500 volts per mil thicknessof coating is desirable.

Another test is made to determine the solvent resistance of the enamelby immersing samples in both alcohol and toluene and determining thechange in scrape value. In many cases a Wire enamel otherwise havinggood characteristics deteriorates to such an extent after being immersedin either of these common solvents that it possesses substantially nomechanical strength. Therefore, the enamel would be unsatisfactory forimpregnation in varnishes using either of these solvents The so-calledjerk test is applied to determine the ability of an enamel coating onWire to withstand such severe uses as in coil winding machines. In thistest, a length of enameled wire is elongated up to 30%, for example, bya sudden Jerk applied thereto and the resulting condition of the enamelcoating is determined. If the coating is uncracked and continuous afterthe jerk test, it is deemed satisfactory. v

A particular test to determine the ability of a given enamel coating towithstand baking temperatures is the heat shock test. In this test, theinsulated conductor is coiled about a predetermined size mandrel a'ndheated in an oven to a temperature of about 125 C. Many wire enamels,when cooled from this temperature, will be found to have cracked orcrazed badly.

A rather severe test is the hot varnish test performed by immersion ofthe enameled wire for at least 20 hours in impregnatlng varnish at atemperature of 125 C. After the test, the scrape value of the enameledwire is made to determine the mechanical toughness and hardness ascompared to its original value. A poor enamel coating will sleeve, ,thatis, become completely non-adherent, or its scrape strength may becomenegligible. l

Since many electrical motors are employed in contact with refrigerants,a desirable characteristic of a high-grade wire enamel is a completeinertness to the usual refrigerants, with or without lubricating oiltherein. The refrigerant is generally heated during the test in order ton simulate the most severe conditions of operation.

In liquid dielectric cooled transformers and other apparatus, theinsulated Wire is subject to the action of hot dielectric liquids such,for example, as oil or chlorinated and/or fluorinated hydrocarbons. Atest to determine whether or not the enameled wire is suitable for thisuse is made by immersing it in the hot dielectric liquid for prolongedperiods of time and then measuring the change in its mechanicalproperties, such as scrape value. A good enamel will have changed verylittle after the test.

From the standpoint of manufacturing the criteria of a good Wire enamelare its ease of application to copper wire, and the baking conditionsrequired to achieve a satisfactory enamel coating.

Some enamel compositions must be baked within an extremely narrow rangeto obtain the optimum properties. The care and control required may beimpractical, since large amounts of waste may be produced by smallinadvertent changes in conditions of baking. Changes in size of the wirebeing enameled, for example, may require considerable changes in thetemperature and speed of travel through a baking tower. A desirablecharacteristic of a commercially satisfactory wire enamel composition isthe attainment of `a, satisfactory cured condition over a relativelywide range of baking temperatures.

In some cases, it has been found to be commercially desirable to producedifferent degrees of coloration of the applied enamel on wire bychanging the baking temperatures. In general, a low baking temperatureresults in a light golden colored enamel coating closely similar incolor to that of the copper wire itself, while with higher bakingtemperatures the color becomes 'progressively redder, and a darkmahogany or black is reached at maximum baking temperatures. In order tosatisfy the requirements of the trade, it is desirable that the enamelbe of a satisfactory chemical and mechanical condition even though itmay be baked to attain any given color, that is, from a golden to ablack.

It will be appreciated that wire enamel compositions may be prepared,without excessive eort, that will exhibit high values as to one or evenseveral of the critical properties desired in a good enamel, but someother property or properties will be so poor that such'composition wouldnot be considered satisfactory Afor commercial use. Those skilled in theart are well acquainted with the extraordinary difficulties involved inproducing a wire enamel ofwhich all the properties are better than fair.

The object of this invention is to provide a reslnous composition4suitable for application to electrical conductors which on treatmentresults in an enamel coating having good insulation characteristics andmechanical strength.

A further object of the invention is to provide enamel composition forapplication to electrical conductors which is copolymerizable over awide range of baking temperatures to provide for a v predeterminedcolor.

A still further object of the invention is to provide an organic coatingon electrical conductors capable of successfully meeting the recognizedtests as herein described to determine the mechanical and chemicalcharacteristics of enameled wire.

Other objects of the invention will, in part. be obvious and will, inpart, appear hereinafter. For a further understanding of the nature andobjects of the invention reference should be had to the followingdetailed drawings of the invention in which:

Figure 1 is a cross section through an insulated conductor.

Fig. 2 is a chart of heat varnish failures plotted against composition.

Fig. 3 is a chart plotting heat shock failures against composition, and

Fig. 4 is a chart plotting the properties of a wire enamel againstbaking temperatures.

According to the present invention, organic compositions highlysatisfactory for use as wire enamel coatings are derived from acopolymerizable combination of urea-formaldehyde resin and a polyesteralkyd resin. We have found that this composition when baked onconductors exhibits the highest degree of hardness, toughness, andflexibility with respect to mechanical requirements and has suchoutstanding chemical resistance that it is almost completely unaffectedby various solvents, such as alcohols and toluene, hot varnish, oils,andhalogenated hydrocarbons.

The proportions of the composition are somewhat critical in order toattain the optimum values of the required characteristics. In particularthe proportion of urea-formaldehyde should be within the limits of about30% to 60% with the alkyd resin comprising the remainder. When thecomposition is outside these proportions, the properties are ratherunsatisfactory.

As is well known in the art of applying enamel to wire, the composition,viscosity of the enamel and other factors may require slight changes asdifferent size wire is being treated. For example, a composition having40% urea-formaldehyde gave excellent results on No. 20 wire, whereas 45%to 50% urea-formaldehyde content gave slightly better results on No. 26wire than a 40% urea-formaldehyde composition.

A typical urea-formaldehyde resin suitable for the practice of thisinvention is the reaction product of 1 mol of urea with 2 mois of formntailed herewith. For use in preparingthecomposition, the clarified and'dehydrated ureal formaldehyde in the solvent soluble stageor theA-stage is dissolved in suitable lsolvents therefor.

A typical solvent is composed of 40% xylol4 and 5 60% butanol. A 50%solids content solution is satisfactory for use. Another solvent iscomposed of a mixture of 100 icc. ethyl alcohol, 84 cc. N butyl alcohol,14 cc. ethyl lactate, and to 10 grams of salicylic acid'. Approximately100l 1o grams of A-stage urea-formaldehyde resin may be dissolved in thelatter mixture.

Urea reacted with polymers of formaldehyde, such as paraformaldehyde,and other aldehydes may be employed in preparing a wire enamel. 15

' The degree of condensation of the urea-aldhyde considered in combiningit with the alkyl polyester resin. i y

The alkyd resin employed in the present wire enamel is composed of amixture of an aliphatic unsaturated alpha-beta dicarboxylic acid or itsanhydride, such as malelc anhydride, and succinic acid. The succinicacid should be less in molar amount than the mols of ethylene alphabetadicarboxylic acid. A mixture of a dihydric alcohol and glycerolproviding approximately the same total number of hydroxyl groups as thecarboxyl groups in the mixture of acids is used in the reaction. 'Iheratio of mois of dihydric alcohol to the glycerol may vary from 1:1 to6:1. From tests made with many alkyd polyesters, it has been found thatglycerol is apparently a necessary ingredient, since it appears toprovide for compatibility of the alkyd resin with the urea-formaldehyderesin. The chain length of succinic acid appears to impart the mostdesirable characteristics from a mechanical strength standpoint. Forexample, the substitution of adipic acid in Example I for the succinicacid causes failure in the heat shock test and diminishes the scrapevalue and alcohol resistance a well. In producing the alkyd polyesterresin the mixture of acids and the alcohols are reacted in a closedreaction vessel equipped with a stirrer, a trap and a gas inlet toprovide for an inert atmosphere free of oxygen. The reactants are heatedrapidly to about 150 C. and the temperature is then more graduallyraised to a temperature of about 190 C. Water is collected in the trapas the reaction proceeds. The reaction is continued for approximately 3to 6 hours to an acid number of from about 75 to 140. The reactionmixture produced is diluted with diacetone alcohol or other solvent,while hot, to a solids content solution.

A Wire enamel solution may be prepared by mixing a 50% urea-formaldehydesolution, for instance, with a 50% alkyd solution in the proportion of60% 'of the alkyd solution to 40% of the urea-aldehyde solution. In somecases, to produce a suitably viscous Wire enamel, the mixture may bediluted with a mutual solvent, which, for example, may be a chlorinatedethane. A

The wire enamel so prepared may be applied by flowing, or by adippingprocess or other suitable method of applying the enamel solutionto a copper conductor. To drive oit the solvent and to cure orcopolymerize the alkyd resin with the urea-.formaldehyde resin, thecoated wire is heattreated or baked. The baking temperatures may bevaried within a wide range. since for most satisfactory application thetemperature must be correlated with the speed of the wire through theenameling tower as well as the size of the tower. In a small high-speedtower, a temperature of approximately 450 "C. may be satisfactory, whilein a large tower with slower wire travel speeds a temperature oi' 250 C.or higher may bev suitable.

Referring to Fig. 1 of the drawing, there is illlustratedan electricalconductor i0 carrying a coating I2 of the heat-treated alkyd-ureaaldehyde resin of this invention. It is believed that ay copolymer ofthe urea-formaldehyde and the `alkydresln is produced. However. we donot known composition available on the market today.

Referring to Fig. 2 of the drawing, there is villustrated therein thecritical relationship of proportion of urea-formaldehyde to a givenalkyd resin for agiven size of copper wire. At approximately 40%urea-formaldehyde a negligible per- 5 centage of the-tests fail whensubjected to immersion for 20 hours in varnish heated to 125 C. Fig. 3is a second curve for the same combination of resins asin Fig. 2 showingthat a critical minimum failure on heat shock is reached when 40% 0urea-foraldehyde is employed. Therefore the solution having a solidscontent of from 15% to 70 tent may be employed, for example, a 50%solids content.

40% urea-formaldehyde resin content appears to produce the best enamel.The composition on which the tests shown in Figs. 2 and 3 weredetermined was prepared from an alkyd polyester 5 produced by reactingthe following:

EXAMPLE I Mols Maleic anhydride 6.10 succinic acid 1.82 Ethylene glycol4.43 Glycerol 2.32

Glycerol 1.34

This polyester was reacted to an acid number of from to 90. A Wireenamel produced by combining 60% of the resin of Example II and 40% ofurea-formaldehyde resin was tested to deter- 75 mine the change in thefour most critical properties with respect to variation in bakingtemperature. These values are plotted in Fig. 4. It is believed that thecharacteristics of the wire enamel shown in Fig. 4 indicate the greatestlatitude in baking known for any Wire enamel. The relatively ilat valuesover the optimum range of baking temperatures shown make it possible toattain any desired color in the applied enamel coating by predeterminedbaking temperature without entailing a sacrice in some property.

The numbers used as the abscissa in Fig. 4 were established by means ofa standard chart made by selecting samples of enameled wire baked atclose intervals over a range of temperatures, thus producing coatings ofvarying degrees of color. The colors are uniformly and progressivelydarker from 1which is practically transparent and of a copper color-to16--which is a dark mahogany. Thus, by baking to the 417`i'lgure, analmost black enamel is obtained. At the 6 value alight orange to goldenenamel coating is produced on copper wire. Intermediate colors areobtained between these two values by appropriate baking conditions.

A large number of enamel compositions were prepared according to thisinvention and were tested for dielectric strength. When applied tocopper wire and baked all the enamel coatings tested above 2000 voltsper mil. Compositions embodying the alkyd polyesters of Examples 1 and2, often gave dielectric strength values of 3500 volts per mil.

It was also found that whereas some enameled wire coatings deteriorateon standing for long periods of time, the wire enamel coatings of alkydpolyester and urea-formaldehyde actually im-i prove in some propertieson ageing for six months or longer. Therefore, the shelf life or storageisexcellent.

The hardness and toughness of the enamel coatings on wire may be said tobe roughly at least three times that of the tung oil enamels used by theprior art.

Indicative of the improvement of the present composition over prior artenamels is the following table of comparative values, all made on agiven size copper wire:

\ chain organic compounds commonly applied in a combination with wireenamels.

Since certain changes may be made in the above invention and ditlerentembodiments of the invention could be made without departing from thescope thereof, it is intended that all matter contained in the abovedescription or taken in connection with the accompanying drawings shallbe interpreted as illustrative and not in a limit' ing sense.

We claim as our invention:

1. A resinous composition composed of, in combination, from 30% to 60%by weight of partially reacted, thermosetting urea-formaldehyde resin,and from 70% to 40% by weight of the partial resinous polyester alkydreaction4 product compound of an acidic mixture of maieic anhydride andsuccinic acid, the mols of maieic anhydride being more than, but notexceeding substantially 3.35 times, the mols of succinic acid, and amixture of glycerol and ethylene glycol vin a molar ratio of from 1:1 to1:6, the mixture of ethylene glycol and glycerol providing substantiallytwo hydroxyl groups for each molecule of acidic mixture, the alkydreaction product having an acid number between 75 and 140.

2. A resinous composition suitable for application to conductors as awire enamel comprising, in combination, from 30% to 60% by weight ofpartially reacted, thermosetting urea-formaldehyde resin, and thebalance composed of the partial resinous reaction product of 5.28 molsmaieic anhydride, 2.64 mols succinic acid, 5.91 mols ethylene glycol and1.34 mols glycerol, the reaction product having an acid number ofbetween 75 and 140.

3. A resinous composition suitable for application to conductors as awire enamel comprising, in combination from 30% to 60% by Weight ofpartially reacted, thermosetting urea-formaldehyde resin, and thebalance composed of the partial resinous reaction product of 6.1 molsmaieic anhydride, 1.82 mols succinic acid, 4.43 mols ethylene glycol and2.32 mols glycerol, the reac- Table Solvent Resist- Scrape Vnlue valncesggpe Aftier Ilin' a ues er mers ng 00 Sample No. Scrape Jerk Heat hoursin HOP C. 67 Hrs.

Shock Varnish Halogenad Hydrocar- Alcohol Toluol bons (l) Tung Oilenamel 15 OK-Slight Cracks. Fails.. 5 7 Sleeves.. 3 (2) Polyvmyl resmenamel 29 OK-- OK..- l5 29 OK-26. 20 (3) Example I Composition.- 30 0K.28 27 OK-28. 28 (4) Example Il Composition -30 OK... 27 31 OK25. 27

herein may be employed for producing a suitable wire enamel solution.The solvents may be selected by reason of availability and cost.

In order to provide for even greater flexibility to meet certain extrememechanical requirements,

tion product having an acid number of between 75 and 140. 4. An enamelsuitable for applying to conductors comprising as the resinouscomponent, from 30% to 50% by weight of partially reacted, thermosettingurea-formaldehyde resin and the balance composed of the partial resinousreaction product of 6.1 mols maleic anhydride, 1.82 mols succinic acid,4.43 mols ethylene glycol and 2.32 mols glycerol, the reaction producthaving an acid number between 75 and 140, and a solvent for the resinscomposed of diacetone alcohol, butanol and xylol.

5. An electrical conductor provided with a hard, tough, exible andsolvent resistant coating comprising the heat-teated polymer product offrom 9 30% to 50% by `weight of partially reacted thermosettingurea-formaldehyde resin, and the balance composed of the partialresinous reaction product of 5.28 mols maleic anhydride, 2.64 molssuccinic acid-,5.91 mols ethylene glycol and 1.34 mols glycerol, thereaction product having an acid number between 75 and 140.

6. An electrical conductor provided with a hard, tough, flexible andsolvent resistant coating comprising the heat-treated polymer product 1oof from 30% to 50% by weight of partiallyreacted, thermosettingurea-formaldehyde resin, and the balance composed of the partial'resinous reaction product of 6.1 mols maleic anhydride,

1.82 mols succinic acid, 4.43 mols ethylene glycol and 2.32 molsglycerol, the reaction product having an acid number between 75 and 140.

CHARLES B. LEAPE. FRANK A. SA'ITLER.

0 REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,195,362 Ellis Mar. 26, 19402,238,685 Ellis Apr. 15, 1941 2,255,313 Ellis Sept. 9, 1941 OTHERREFERENCES Synthetic Resins, pages 57 and 58, published 1944 by ResinousProducts and Chemical Co., Phila., Pa.

Hodgins et al., pp. '1 and 8, Paint,.Oi1 and Chemical Review, June 22,1939.

